1. Field of the Invention
The invention in general relates to dielectric resonators for microwave circuits, and more particularly to a dielectric resonator which can be tuned by non-mechanical means.
2. Description of related art
Dielectric resonators are often used as frequency determining elements in microwave circuits. Such dielectric resonators are of relatively small size and exhibit low noise, high efficiency, high temperature stability and reliability. Various types of dielectric resonators are used for governing the frequency in oscillator circuits for microwave systems such as radar, communication links, navigation and electronic warfare, by way of example.
The dielectric resonator, operable at a particular frequency, is tunable over a narrow bandwidth and frequency fine tuning must be accomplished without affecting the high Q of the resonator. In addition, vibrational immunity is necessary for intended low noise applications such as required for stable oscillators.
Many dielectric resonators include a dielectric member which is generally positioned within an enclosure, and frequency tuning of these resonators include changing the dimensions of the enclosure or inserting metal or dielectric rods into the enclosure. This mechanical link from the inside of the enclosure to the outside of the enclosure would objectionably increase vibrationally induced, resonator frequency instabilities.
Non-mechanical tuning includes the use of ferrites with an accompanying magnetic field which is varied, as well as utilizing photosensitive material on the dielectric member and illuminating the photosensitive material to change its conductivity and perturbate the electromagnetic field in and around the dielectric resonator.
The present invention provides for a non-mechanical tuning of a dielectric resonator, which is relatively simple and which does not affect the high Q of the resonator, particularly when the resonator is operated at cryogenic temperatures.